The idea was telling only those voters in certain counties (who predictably would vote a certain way) to vote; i.e., a less-blatant version of telling exactly the subset of people who are registered to vote for a given party, to go out and vote. That is a partisan action.
Perhaps, but it'd then just be on the same level as any other broadcast medium that puts out such a message. I presume the more partisan of the cable news channels are still allowed to say "hey everyone, vote!"?